DE1285455C2 - POROESE FILTER MATERIAL WITH ULTRA FINE PORE AND METHOD OF MANUFACTURING - Google Patents

Description

The invention relates to a porous filter material with ultrafine pores of essentially all diameters less than 25 microns, consisting of a relatively large base Pores on which, with the interposition of an anchoring layer, a finely divided, fibrous material is deposited.

A filter material with the pore size mentioned is already known (German patent specification 933 447), which has a large-pored base and a fine-pored filter layer attached to it. the The base consists for example of fibers of cotton, cellulose, polyamide or glass, and the fine-pored layer consists of an easily removable suspension or a separate, replaceable one layer

Mixtures of asbestos with diatomite and cellulose have also already been proposed as filter material (German Patent 939 446) and the use of a binder to fix the fibrous ao Materials on the basis (U.S. Patent 2,694,660).

Filter materials made of cellulose elements with a pore size of 2 to 25 μ are also made "Chemical Engineering" of June 13, 1960, pp. 209 to 212, known, and filter materials made of glass fibers with 9.35 to 0.5 μ and i * as incorporation of short-fiber Asbestos are mentioned in the journal "Chemie-Ingenieur-Technik", Volume 26, 1954. No. 4, pp. 221 to 224, ^ ktrSniisches filter material with a porous space of 43% and about 0.8 μ pore size is finally through the prospectus of the Schuhmacher company see Fabik Bietigheim / Württ. No. 3000.1.59. with the Trade name Diapor already known.

The processing of glass and asbestos fibers to form a dust filter is described in the German utility model 1720 057 mentioned and a fiber bond with plastic in a filter material is off the German utility model ι 760 923 known

Furthermore, membranes made of fluorochloroethylene resin are known, the manufacture of which takes place from a 20% solution with 34% Fe 3ten components after dilution with xylene using a spray gun on a stainless plate treated with silicone mold ^{release agent and subsequent exposure to heat at 250 C for 10 minutes;} a second and third step can be achieved analogously (Houben-Weyl, I / l, p. 660).

Finally, membrane filter sheets are used for disinfection and hitherto known in pastures Cardboard serves as the carrier material. They are suitable because of their good mechanical resistance Stress for technical filtration. Her mean pore diameter can be 0.25 to 0.5 · α accordingly, the filtrate output is V ei

As evidence of technical progress, reference is made to the following table:

sample Filter material Pore size Material in the filter layer resin
binder Substrate
or sluggish / (Micron) A. invention
(Ultipor. 1) 0.1 Crocidolite asbestos
(Fiber web) Neoprene none B. invention
(Ultipor. 35) 0.35 Crocidolite asbestos
(Fiber web) melamine Glass
paper 1 Ceramic
(Selas Candle No. 3) 0.51 Ceramics none none C. invention
(Ultipor. 75) 0.75 glass fiber
(Rail) melamine none 2 Membrane type
(Millipore »AA0 0.8 Cellulc ^ eester film - none 3 Membrane type
(Gelman GA-4) 0.8 Cellulose triacetate film - none D. Invention '
(Ultipor. 9) 0.9 Mixture of fiberglass and
Diatomaceous earth (orbit) Epoxy Cellulosic
paper 4th Fiber type
(Ertel filter
Pad no.EO 13167) 1.36 Mixed cellulose and
Asbestos fiber
(Plate) melamine 5 Fiber type
(HoUingsworth & Vose
H-931 E) 4.5 glass fiber
(Rail) acrylic none 6th Filter paper
(Whatman No. 4) 15.1 Cellulose
(Baiin) none none

i 285 455

100 cm ² filter area 3 to 20 ml in one second at a pressure of 70 cm HgS (brochure "Selecta-Filtrier-Papiere", around 1960, p. 16).

The manufacture of membrane fibers with a pore size of 0.1 μ is also known, whereby collodion wool is used as the filter material (German Patent 329 117).

Furthermore, coating layers for filter layers are known which have fiber components, which as a result Hegen an embossing action at an angle of more than 30- to the base, with the intersecting Fibers created by the embossing, but essentially only parallel to the base form extending network with a void volume (German Patent 736 283).

The invention is based on the object of creating a filer which, with a uniform pore size of less than 10 μ, has a large cavity volume U-.! thus a relatively low flow resistance au I ¹ - * eist.

According to the invention, the filter material is thereby gi .; cnnzeichnet that the finely divided material which contains at least 25 ⁰ Zo fiber having such a large Anvil of fibers at an angle of nu: r than 30 ^ are the foundation and, together with fibers at ■ -rer inclination Wink »· that a network mi 'a void ^{volume of at least 75 0} O gc ¹ · Idet, wherein the layer has a maximum Pi ... ^ diameter of less than 10 μ.

i) the method of manufacturing the filter material n .; H of the invention is üadurc.x characterized that .ι then on the lilac-shaped fiber mate

rial-containing anchoring dispersion applies a coating dispersion and that by selecting the flocculation properties of at least the dispersion liquid of the coating dispersion to dewater lumps of the particulate fiber material forms and separates the lumps as a microporous layer adhering to the porous base, in which a portion of the fibers ii_ make an angle extends more than 30 ° from the base and

ίο with fibers from other angles of inclination against the Base area forms a cavity volume of at least 75%, which does not have any larger pore diameters than 10 μ.

While in the usual manufacturing process for filter paper the precipitated on a basis Fiber layer, which is partly stripped off as a self-supporting layer, made of fibers which are sucked onto the base via the suction boxes, with the result that the fibers lie essentially in planes parallel to the base, the coating layer, which in the process according to the present invention is applied to the base, a structure in which some of the fibers are arranged at an angle of 30 ° or more to the base.

The "fact that when following the procedure Filter materials produced according to the invention are fibers with angles of 30 ° or more to the base can be easily determined using a microscope; in this way was also through Investigation of layers produced according to the invention found this special property

total
Weight
4 / 9.3 dm ¹ ) thickness
(not
pressed)
(mm) Thickness (with
4.2 kg / cm »
pressed)
(R.A.M) fracture
load
at train
(kg / 2.5 cm
Broad) fracture
strain
(%) Air flow
(l / min per 9.3 dm ¹
Area at Ap of
50.8 cm
(Water column) Water flow
(l / min per 9.3 dm ¹
Area at Jo of
0.3S kg / cm ') Pressure drop Ap
(cm water column)
with an air flow
of 30 l / min each
9.3 dm ¹ area 7.9 0.46 0.168 1.59 3.7 198 12.5 980 6.3 0.43 0.223 1.04 0.5 2266 92.7 *) 292 1000 4.6 4.6 very high - 1.7 0.19 1196 2.2 0.165 0.086 1.36 0.5 13027 1136 104 4.5 0.165 0.137 1.36 5.1 750 66.2 556 2.0 0.14 0.104 0.68 1.0 1204 90.8 744 52 1.52 1.3 54.4 1.3 56.6 132.5 157 110 2.54 2.03 5.35 2.8 62.3 1.06 444 6.3 0.46 0.14 1.77 3.0 3058 56.8 135 8.8 0.23 0.18 5.44 1.1 3909 359.6 40.1

·) Converted to 100 cm ¹ filter area, a filter material B with a pore diameter of about 0.35 microns at 70 cm HgS, instead of the 92.7 specified above for other dimensions, can penetrate 15.5 l / min of water.

In the table there are four "Ultipor" strips (samples A to D), arranged according to pore size conventional materials (samples 1 to 6), which both from the groups of ceramic media, membranes and fiber materials are selected; here each is the Comparable products the best material available on the market.

This information proves that the filter material According to the invention, for a given pore size, a higher proportion of open areas (pore volume or void volume) than the comparison products. This is clearly evident from the aerial and Water flow rates at a given pressure drop across the filter or at the pressure drop in the Filter at a given air velocity through the filter. Both a higher flow rate and a lower pressure drop show the higher proportion of free spaces or a higher pore volume. »°

These parameters are to some extent dependent on the thickness of the material; the thicker a material the greater the pressure drop through this material for a given pore size. The filter material according to the invention has a lower pressure drop than that for a comparable pore size known filter materials of the same or even significantly smaller thickness.

The comparison with the ceramic filter (sample 1) with a pore size of 0.51 μ shows that the materials A and P with pore sizes of only 0.1 and 0.35 μ higher air and water flow rates at the given pressure differences or a lower pressure drop at the given Have air flow rate.

Compared to the two membrane filters (samples 2 and 3) m ^; t per 0.8 μ pore size, the filter material C with 0.75 μ pore size shows a much higher air and water flow rate as well as a lower pressure loss for a given air flow rate; Even the filter material B according to the invention with only 0.35 μ pore diameter shows a higher air and water flow rate and a lower pressure drop than the comparison materials 2 and 3. Furthermore, the filter material D according to the invention with 0.9 μ pore size shows which is about ten times as thick as comparative samples 2 and 3, a greater water flow and a significantly lower pressure drop, with a further decisive advantage that the material according to the invention is many times stronger than the membranes of the prior art.

When Samples C and D are compared with fibrous materials 4 and 5, which are noticeable If the pores have larger pores, the values of the filter material according to the invention are almost always more favorable; this is particularly noticeable for the comparison of sample C with the comparative product 5 (6-fold Pore size) with regard to the approximately 4-fold air flow rate and the 20-fold water flow rate as well as the lower pressure drop with roughly the same strength. In addition, the material D, which is in its thickness is between the comparison products and 5, compared to these a multiple strength having.

Finally, the comparative sample 6 represents a typical filter paper which, despite its porosity, which is many times that of the investigated products, has a remarkably low flow capacity despite its small thickness: Material C with only one twentieth the pore size and about SgWChS ^ Thickness shows flow rates for air and water which are a multiple of the values measured for the known filter material. For the practical use of the filter materials according to the invention, the following is also of importance: For many applications, the emphasis in recent times has been on filter bodies with a large surface area and at the same time a small volume, for which it is necessary to widen the filter web. Up to now, this has been a very difficult problem in the case of small-pore filters because the filters available were suitable for corrugating flour. Are ceramic filter had in the form fvelche they should have later, prefabricated membrane filters are not sufficiently flexible and elastic for the curl, -id you herkommhcnen fibrous materials are za thick. Of the filters with a small pore size (below 1 μ) given in the table, only the filter materials according to the invention are suitable for corrugation

The compressibility is a measure of the free Volume of filter material; the filter materials according to the invention are the comparison products 2 up to 4 also superior in this respect nor that they complain faster and significantly Costs can be produced as a: iitermaterial of the membrane type. In addition, the use of a wide variety of fiber materials and Synthetic resins are much more adaptable to the requirements of flexural strength, chem ^ chen Resistance, wettability and temperature!

The use of a binder known per se in the method according to the invention l · 'of Significance in order to maintain the high cavity volume according to the invention. If you get the 1 asern not determined in the positions which they happen to be take when laying the flakes and including a proportion of fibers with an angle of 30 * and when the basis is understood, they became obvious when used later Reasons not to remain in this position. The natural tendency of the fibers is to become compressed and in this way to be brought into a plane parallel to the base, thus making the structure a layer which does not contain any binder is destroyed

would. ,,,,

In a further embodiment of the process, according to the invention, at least one of the dispersions is used a fiber material, which fibers with an average diameter between 0.005 and 2 μ and an average fiber length between 5 and 1000 μ.

The degree of flocculation with which the desired Uniformity, the desired adhesion and the desired void volume will be obtained determined using the test described below for each dispersed system. The The method according to the invention is made possible using coarse filter media such as papers and nonwoven nonwovens, to microporous media by depositing a layer with the desired, ultrafine or microporous dimensions and the desired void volume on this.

The void volume of the microporous layer exceeds 75 ° / "and is often more than 85 ° /".

Filter bodies equipped with the microporous material according to the invention allow the absolute distance of particles that are 10μ in size and even particles of 0.05μ and below from flowable media.

The method according to the invention is particularly suitable for use in connection with porous Foundations that come in a folded, coiled, or curled shape. The porous base can in these cases from a resin-impregnated cellulobe-like Material are formed. The microporous layer can be based on the procedure be deposited without bridging between adjacent folds, turns or corrugations he follows; shrinkage of the microporous layer does not occur. Preferably the porous Base material has an average pore diameter of not less than about 2.5 μm. Such Materials naturally contain larger pores, such as those of 20 to 25 μ or more.

The dispersion liquid is preferable to the finely divided fiber material and the base material neutral. It is also not intended to solve these in a substantial amount, albeit at re-use of the dispersion liquid the fact that some material is in solution, is not a disadvantage, as a saturated solution quickly forms at the beginning. The dispersion liquid should be volatile at an appropriately elevated temperature below the melting point of the fiber material, to facilitate removal after the dispersion has been deposited. Under certain conditions you can however, non-volatile dispersion liquids are desirable; these liquids can be removed, by washing them with a volatile solvent which is a solvent for the dispersion liquid but not for the fiber material. The liquid to be filtered with the end product can also be used as the dispersion liquid.

The desired properties of the deposited fiber layer can be controlled by various Determine more variably.

One factor is the size of the fibrous material, which can be chosen to be larger than, equal to, or finer than the pore diameter of the base. The degree of flocculation of the dispersion is an important factor in determining whether fiber particles are retained on the surface of the base or whether ία penetrate the pores. If the dispersion has a high degree of flocculation, all fiber particles will be retained on the surface. When the fiber particles are dispersed , the particles that are finer than the base pores tend to enter the pores and, in fact, pass through them.

As mentioned above, the degree of flocculation is important in terms of void volume, uniformity and adhesive properties of the microporous layer. It is believed that, with the degree of flocculation in the optimum range, a number of fibers in the dispersion will clump as the fibers will tend to cling to each other the first time they touch and maintain the disordered orientation thus obtained . Instead of the individual fibers, the lumps are then deposited onto the porous base. There can also be a proportion of fibers at an angle of more than 30 °, since the fibers in the dispersed clumps occupy this position and retain this position after the deposition after they are held in this position by the other fibers. Since the fibers, while still dispersed, are combined with other fibers, there is a tendency to combine at a greater distance than would otherwise be obtained, resulting in the *

ίο unusually high void volume of the microporous Contributing media according to the invention. The extent to which the flocculant and deflocculant (which are not required if the dispersion has a sufficient degree of flocculation even without it) are necessary and in which one has to control the pH value and the movement in order to achieve the optimal flocculation state to obtain with any fiber material and any basis must be determined in the experiment by using the test described here

ao the dispersion flocculants and deflocculants adds and changes the state of motion and the pH of the dispersion.

It can be advantageous to establish a blockage in with a mixture of small and large fibers

»5 to support the pores and a suitable one Surface coating. Any significant impregnation (i.e., greater than about 25 to 100 microns below the surface) of the porous base, however, is preferably avoided as such penetration easily leads to a decrease in the permeability of the porous base.

As mentioned, it is important that the finely divided, fibrous material be firmly secured after application is held on the porous base and after application neither passes nor through the base Counter pressure or mechanical abrasion is easily shifted.

So that the product can withstand a countercurrent and mechanical abrasion, to achieve a strong adhesion between the porous base material and the fine-particle, fibrous material deposited on it, the base is first coated with an anchoring dispersion in the form of a liquid or liquefiable binder and a particulate material which is composed of the binder is wetted, treated. Thereafter, the covering or coating dispersion of the above type is applied and the entire product is treated by heating, or in some other way, so that the binder binds the particulate material to the porous base.

Fibrous materials are used in the anchoring dispersion. These should be capable of being suspended in a flowable medium and of forming a mat , the pores of which are finer than those of the basis on which they are deposited, and preferably finer than the pores of the microporous main layer. The anchoring layer can, but need not be, contiguous . Fiber- like materials for use in the anchoring dispersion have an average diameter of about 0.005 to 2 μm and an average length of about 5 to 1000 μm , preferably an average diameter of about 0.01 to 0.5 μm and an average length from about 15 to 500μ.

Non-fibrous materials can be used in the anchoring dispersion, however, one can use

309621/406

V - V:

also at least 25% of the total weight of the particulate Materials used on a fibrous material to maintain sufficient strength and to prevent the anchoring particles from entering the pores of the Enter the basis. If non-fibrous materials are used, they are preferably with an average diameter of 0.01 to 1 μ used.

The fibrous and / or non-fibrous, particulate materials in the anchoring dispersion should be capable of, through the liquid or liquefiable binders to be wetted and by this itself in the presence to remain wetted by the dispersing liquid. The latter requirement can generally be met, by adding the binder and particulate material prior to adding to the dispersant Liquid mixes.

The finely divided material that is used for the anchoring layer can be the same as the particulate Material used in or different from the coating dispersion.

The binder used in the anchoring dispersion must be liquid or at the time of the Bond liquefiable and then solidified, such as through polymerization, crosslinking, evaporation a solvent, cooling or the like. Be capable. Liquid thermosetting resins are special Advantageous, as they are effective in low concentrations are and can be kept in liquid form until their solidification is to be carried out. Typical liquid thermosetting resins include phenol-formaldehyde resins, urea-formaldehyde resins, Melamine-formaldehyde resins, polyester resins and polyepoxy resins.

The liquid polyepoxy resins are particularly preferred. The polyepoxides for the purposes of the invention can be saturated or unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic, if desired, substituted with substituents such as chlorine atoms, hydroxyl groups, ether residues and the like being. They can also be monomeric as well as polymeric in nature.

Suitable binders for the purposes of the invention solutions of solid, thermosetting resins in suitable solvents are also possible.

Thermoplastic, solid binders can also be used as long as they can be softened or liquefied into a tacky state , such as by heating above their softening point, to effect the bond. Such thermoplastic materials can be used alone or in solution in an appropriate solvent. Zn typical thermoplastic binders include polyethylene, polypropylene, polymethylene, polyisobutylene, polyamides, cellulose acetate, ethyl cellulose, copolymers of vinyl chloride and vinyl acetate, polyvinyl chloride, polyvinylidene chloride, PolyvinylbiJyraL PoIytetrafluoräthylen, polytrifluorochloroethylene, lignin sulfonate, resins, starch binder Caseinbindemittel and terpene resins, polyacrylic resins, such Polvmethyimethacrylat, alkyd and synthetic rubbers such as butadiene-styrene polymers.

As a dispersing, flowable medium for the production of the anchoring dispersion, any flowable medium can be used which is neutral under the conditions of use, like all the flowable media suitable for the coating dispersion.

In the preparation of the anchoring dispersion, the binder is preferably used with the finely divided Material mixed and the mixture then added to the dispersing liquid with agitation to obtain a stable dispersion. When the finely divided material in this way with the binder is prewetted, the droplet size of the finished dispersion is coarser than when the fine-particle dispersion is added separately Material and the binder to the dispersing, flowable medium. For stabilization this coarser dispersion becomes. '' ne viscosity of the Ready-to-use dispersion of over 40 oC at 25 ° C

is preferred. If the finely divided material dispersing, The fluid medium does not have a sufficient viscosity for this, one can determine the viscosity of the dispersion by adding the known, soluble, high molecular weight Substances that increase the viscosity of flowable media, even in very small quantities able to increase significantly. When the dispersing medium is water, soluble cellulose derivatives are particularly suitable. The addition of less than 2 percent by weight more soluble, high molecular weight

Hydroxyäthylceliulosc, soluble sodium carboxymethyl cellulose or soluble hydroxypropylmethyl cellulose to water e.g. B. increases the viscosity of the Water well above that even in the absence of the particulate material and binder Minimum value.

An alternative method for making the anchoring dispersion, with sufficient wetting of the finely divided material by the binder can be ensured, consists in the use of a dissolved in an appropriate solvent Binder. The binder is insoluble in the dispersing, flowable medium, while the Solvent is soluble in it. The particulate material and the binder solution (which, if desired, may be wholly or partially premixed) become the dispersing, flowable medium added. The solvent dissolves in the dispersing medium and thereby causes precipitation of the binder on the fibrous material.

The viscosity of the flowable dispersion is sufficient to prevent any binding agent or finely divided material from settling before it is applied to the porous base.
The anchoring dispersion should preferably be about

0.1 to 5 parts by weight of finely divided material per 100 parts by weight of liquid and in particular at least about 200 parts by weight of binder per 190 parts by weight of finely divided material.

The anchorage dispersion should be applied to the porous base in a sufficient amount, by about 5 to 50 g of binder per square foot (9.29 dm *) To deposit the surface of the porous base. After applying the anchoring dispersion to the

The upper coating dispersion is applied on a porous basis.

The pore size and the void volume of the microporous covering layer, which is applied to the anchoring layer, depend on the fiber

⁶ S läbgc and diameter as well as the suspension state of the fibers in the coating dispersion. The state of suspension that is required to form a given fiber or mixture of fibers

I 285 455

a layer of the desired pore size and the desired void volume is required by The attempt is determined and the parameters required to repeat the successful attempt can be determined obtained by a few simple measurements.

The suspension state of the dispersion found to be desired is based on the degree of flocculation Determination of the dispersion by titrating with a solution capable of flocculating the dispersion, like magnesium sulphate or aluminum sulphate solution for fiber dispersions with a pH value above about 7 or sodium carbonate or sodium hydroxide solution for fiber dispersions with a pH value below 7. For the fiber dispersion in the test solution is a fiber concentration of 1 g / l and one for the titration solution Active ingredient concentration of 5% advisable. The extent of the obtained with this flocculant Flocculation is determined by observing the turbidity of the dispersion with a colorimeter during the Titration determined. One then has the knowledge that a dispersion with the and the determined Turbidity possesses and can have the correct flocculation properties or the correct state of suspension adjust to this turbidity for the following dispersions. Any desired flocculation property can be selected by adding, according to the amount of titration solution used in the test adjusts the corresponding amount of flocculant or dispersant to the required turbidity and thereby the degree of flocculation increases or decreases.

To reduce the degree of flocculation of the anchoring and / or coating dispersion can be added to both dispersants. To the stronger Flocculation of an anchoring or coating dispersion you can add a flocculant.

Also, amount and location of the fiber particles deposited can be steered by the deposition is affected by change in the size of the particulate material introduced or the amount of movement, which is subjected to the slurry during deposition.

If a coating dispersion tends to flocculate when the suspension is at rest, it can be dispersed by agitation. Once the agitation ceases, as with application to the base, the instability of the slurry leads to deposition. Such a dispersion can thus be applied by means of a moving plate which has openings and is held close to the porous material so that the turbulence results in a fine dispersion which, after application, settles when the movement is less or no longer there is movement .

In order to achieve the highest flow rate or permeability, if there is any impregnation of the porous base at all, any amount and depth of impregnation should be as low as possible. Penetration of finely divided fiber material into the porous base over a depth of the order of two or three fiber diameters or about 100 μ should be avoided in order to avoid a reduction in the speed at which the flow through the porous base is. The flow rate changes directly with the ratio of the void volume to the fiber volume, ie the percentage of voids present. The presence of the anchoring layer tends to essentially avoid any impregnation of the base and thus any reduction in the void volume of the porous base and thus leads to an increase in the flow velocity.

If a dispersant and flocculant is used, the agents should be used with care because if the amount of dispersant is too large, the finely divided material becomes the porous material just happened while using one too

ίο large amount of flocculant the dispersion is unstable and the finely divided material does not form a suitable coating. The relative amounts in relation to the particles and their size, the deposition temperature, the hardness of the water, the solids content of the dispersion and the pore opening of the base can, however, be determined in each case by experiment. Usually prove 0.001 to 5 ° / ₀ dispersants, 0.001 to 5% flocculant to be satisfactory. You can use these means, as described above,

»O use separately or together in the slurry in such quantities that until separation a dispersion is obtained.

A wetting agent can be incorporated into each of the dispersions, of which 0.001 to 5% is usually sufficient and which can be anionic, nonionic or cationic.

The application of the dispersion to the porous base can be done by any method, with which the dispersion liquid is made to flow through the base. You can z. B. on the Dispersion act a pressure difference! Asssn, by applying pressure directly on the dispersion or by applying a vacuum to the underside of the foundation can act. Once the anchoring layer is deposited, it helps to create a Prevent passage of solids in the coating dispersion.

The compressibility and thus the "bulk density" (apparent density) of the microtor-like layer can be changed by changing the pressure difference acting on the layer during the deposition. The pressure difference in turn depends on the speed and viscosity of the dispersion liquid and the permeability of the porous base. For a given pressure differential, the layer thickness can be reduced by incorporating a small amount of bulky or curled, coarse particles which are able to support the finer particles and make them better off .

Io certain cases it is desirable to keep a shrinkage of the microporous layer during drying as low as possible, in order to avoid e.g. B. to prevent throwing or warping of the filter material or to avoid detachment of the applied layer from the wave troughs when the coating is applied to folded paper. The shrinkage can be made minimal by the coating dispersion in several, z. B. applies two to six work steps to the base, while the element is removed from the suspension between the coating passes and exposed to a pressure difference of up to about 7 atm. Larger pressures are avoided before the solidification of the binder in order to avoid any

possible orientation of the angularly oriented fibers to prevent. If a liquid binder is present in the coating dispersion, it can, if desired, between the different order processes for

to be brought to production. On the other hand, solidification can also take place after complete application.

A binder is applicable in conjunction with the microporous coating layer (s) and is preferred. You can apply the binder through the coated base in one finish let flow or one of the above-mentioned binders of the coating dispersion prior to application to put on the foundation. A binder that has an adverse effect on the dispersion can also be used after incorporated into the deposition of the microporous layer. It can e.g. B. after peeling off the flowable Medium washed through the layer or deposited on the surface of the microporous layer from which it spreads through all layers by capillary action.

After the complete application, the bond is effected. The required conditions change mi? the nature of the binder. You can z. B. ^ao the temperature to a value sufficient to increase that crosslinking or polymerization of the binder

Void volume - 1Ö0

definitely. The microporous materials according to the invention, calculated in this way, preferably have microporous layers with a void volume of at least 75% and in some cases 90% ^and even more.

The pore size or diameter of the microporous materials according to the invention is determined according to the procedure of U.S. Patent 3,007,334

The following examples serve to further illustrate the invention.

· ' In game 1 means occurs or the solvent in which the binder is dissolved evaporates. On the other hand, when using a thermoplastic paint as a binder, increasing the temperature can cause the binder to soften or melt. A catalyzed resin can be left at room temperature until it has solidified. Floorboard between the microporous layer and the porous! The adhesion obtained on the basis is very strong, and the result is that the strength of the end product depends mainly on the strength of the porous base.

The void volume of the microporous layer is determined by making the layer according to the invention z. B. on a paper disc of known weight and thickness, whereupon the Weight of the microporous layer and the weight difference is determined. To determine the apparent By volume of the microporous material, the area and thickness of the layer are measured. The real one Volume is determined by immersion using a flowable medium. The void volume is then according to the equation

actual volume of the layer \
apparent volume of the layer /

To prepare an anchoring dispersion, mix 20 g of a liquid binder (a liquid polyepoxy resin in the form of p-aminophenylethyl chlorohydrin, containing 30 percent by weight of cyanoethylated, primary, aliphatic polyamine as hardener), 2 g of butyl carbitol (thinner for the resin) and 2 g of potassium titanate -Fibers (on average 0.5 μ diameter and 50 μ length) and disperses the mixture in 600 cm ^{3 of} water, which contains 0.5 percent by weight of hydroxypropylmethylceUnlose.The dispersion obtained has a viscosity of over 50 ocP and an average droplet size between 50 and 100 μ.

To prepare a coating dispersion, 6 g of amphibole-asbestos fiber of the amosite type are mixed (0.5 x 200 μ), 6 g of the binding agent used in the anchoring disperston, 60 g of butyl carbitol, 12 g Sodium carbonate and 0.6 g of a water-soluble, organic dispersant ("Tarool 850") and disperses the mixture in 61 water. The received Dispersion is an emulsion with an average drop size of 1 to 2 μ.

The anchoring dispersion is then allowed to flow through a paper base with a surface area of 9.3 dm * (average pore size 10 μm) by adding the underside of the foundation a vacuum. of 381 mm HgS. Then the coating dispersion will flow through the base in the same manner.

The base is then heated ^{to 191 °} C. in an oven in the presence of air for 40 minutes.

The microporous material obtained has a maximum pore diameter of 7.5 μ. an average pore diameter of 3 microns and a water permeability of 0.7 l / min dm ¹ (1.5 gallons / min / square foot) with an applied pressure differential of 0.07 at. When the pressure is applied in the opposite direction, it is found the adhesion between the particulate materials and the paper base is sufficient to withstand a pressure of up to 0.7 at. The void volume of the microporous layer is determined to be about 90%. A microscopic examination of the surface of the microporous layer shows a proportion of fibers extending outwards from the base at an angle of at least 30 °.

Example 2

It is a cylindrical, axially pleated ^! Terelement made of a eqoxyharzimprägnierten paper having an average pore diameter of more than 10 μ The thus prepared element is then input into a container that contains the anchoring dispersion from Example 1 through the outlet opening for outflowing material is then a vacuum of 381 mm HgS was applied to draw the dispersion through the paper and cause the particulate material and binder to deposit on the outer surface of the element.

The coating dispersion from Example 1 is then passed through the paper in four separate operations drawn, applying approximately 25% of the total amount in each operation and a vacuum of 0.98 at.

After the entire coating dispersion has been applied, the element moves from the outside to the inside 5 minutes of hot air of 343 ° C passed through it drying the element and curing the resin.

The filter element obtained has a maximum pore diameter of 7.5 μ, an average

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Pore diameter of 3 a and a water permeability of 0.33 l / min dm * with an applied pressure difference of 0.07 at. The adhesion is sufficient to withstand a pressure of up to 0.7 at in the opposite direction, and the void volume of the microporous Layer is about 90 ° / ₀ . A microscopic examination of the element surface reveals a proportion of fibers extending outwardly from the base at an angle of 30 °.

Example 3

To prepare an anchor dispersion 20 g of a solid Polyepoxydharzes (obtained by reacting bisphenol A with epichlorohydrin in an alkaline solution, melting point 125 to 135 C, viscosity: 18 to 28 P, determined on a 40gewichtsprozentigen solution in butyl carbitol in 25 ^C C: epoxy equivalent 2000 to 25,000), which contains 25 percent by weight of m-phenylenediimine as a hardener, 60 g of butyl carbitol, 400 mg of silicon dioxide (average particle size 0.02 μ) and 80 mg of a 10% aqueous solution of a mixture of surface-active agents (potassium oleate and sodium dioctyl -sulfosuccinate) mixed. The resulting mixture, an emulsion with an average particle size of 1 to 5 μ, is then added to water in which 2 g of chrysotile asbestos (on average 0.01 × 50 μ), 0.8 g of sodium carbonate and 0.1 g of tamol 850 «are dispersed.

To prepare a coating dispersion, first an emulsion between 12 g of the same polyepoxy resin, 6 g of butyl carbitol and 1 g of surfactant formed. This emulsion (average Droplet size 1 to 2 μ) is added to 61 g of water, the 6 g of the same chrysotile asbestos contain. The two dispersions obtained are then passed one after the other through a paper base with an average pore size of 10 μ and a surface area of 9.3 dm *.

The anchoring dispersion is applied at the pressure difference that results from applying a vacuum of 381 mm HgS to the base, and the coating dispersion is applied in four parts at a pressure difference of 4.2 at, with air between the applications through the base of 4.2 at can pass through. Then hot air at 343 C is passed through the base for 3 minutes at a rate corresponding to the volume of 15.2 l / min dm *. The microporous product obtained has an average pore diameter of 0.02 α, a maximum pore diameter of 0.8 μ and a water permeability of 0.004 l / min dm ² at an applied pressure difference of 0.07 at. Its adhesion is sufficient to withstand one pressure of 0.35 at in the opposite direction. The void volume of the microporous layer exceeds 85%. The outwardly extending fibers are observed on examination.

Example 4

An anchoring dispersion is prepared by adding 30 g of a solid polyepoxy resin ( by reacting bisphenol Λ with epichlorohydrin in an alkaline solution; Melting point 125 to 135 ° C; Viscosity 18 to 28 P, determined on a 40 weight percent solution in butyl carbitol 25 ° C epoxy equivalent 2000 to 2500), which contains 25 percent by weight of m-phenylenediamine as hardener, Mix 40 g of trichlorethylene and 4 g of potassium oleate. The mixture is added to 11% of water and then mixed with 10 g glass fibers with an average diameter of 9 μ and a length of 1000 μ.

A coating dispersion is then prepared by adding 6 g of the same polyepoxy resin, 2 g of the

ίο same amine, 12 g of furfuryl alcohol (a reactive Thinner for the resin, which also acts as a partial hardener), 12 g of butyl carbitol as not reactive diluent, 3 g of an emulsifier (polyethoxylated fatty acid mixture with acrylic radicals, which go back to Kjefernharzsäuren, with a molecular weight about 700) mixed. The The mixture is then made into a dispersion of 4 g of glass fibers (on average 0.2 x 300 μ) in 2 l of water pH 3 (adjusted with hydrochloric acid) added. The receive-

ao emulsion has a drop size of 3 μ.

The anchoring dispersion is then applied by applying a vacuum to it at the of 381 mm HgS obtained through the Grandlage. Then the coating disperser

»5 sion applied in two partial amounts with a pressure difference of 2.81 at. A paper substrate with a surface area of 9.3 dm * and an average pore size of 10 μ serves as the basis. ^{Hot air of 343 °} C. is then passed through the product for 3 minutes at a rate of 15.2 l / min dm ² . The end product has a water permeability of 0.81 l / min dm ¹ with an applied pressure difference of 0.07 at, an average pore diameter of 2 μ, a maximum pore diameter of 5 μ and sufficient adhesion to withstand the action of a pressure of 0, 42 at in the opposite direction. The void volume of the microporous layer exceeds 85 ° / _0th When examining the microporous layer under the microscope, the outwardly extending fibers can be seen.

Claims (4)

Patent claims: 1. Porous filter material with ultrafine pores, which essentially all have a diameter of less than 25 microns, consisting of a base with relatively large pores on which a finely divided fibrous material is deposited with the interposition of an anchoring layer, characterized in that the finely divided material, which contains at least 25 Ve fibrous material in a manner known per se, has such a large proportion of fibers which are at an angle of more than 30 ° to the base and form angles with fibers of a different inclination that a network with a void volume of at least 75 ° / »Is formed, the layer having a maximum pore diameter of less than 10 μ. 2. Process for the production of the microporous filter material with an anchoring layer according to claim 1, wherein a binder is applied to the surface of a porous base applies anchoring dispersion containing and dehydrates it, thereby identifying 309621/466 draws that a coating dispersion is then applied to the anchoring dispersion containing teiichenfömiges fiber material and that by selecting the flocculation properties of at least the dispersion liquid of the coating dispersion with dewatering, lumps of the particulate fiber material are formed and the lumps are deposited as a microporous layer adhering to the porous base a proportion of the fibers in a win ^la angle of more than 30 ° is developed a basis for! and mi: fibers from other angles of inclination against the base a cavity volume voa forms at least 75%, which does not have a pore diameter larger than 10 μ. 3. The method according to claim 2, characterized in that at least one of the dispersions a fiber material used, which fibers with an average diameter between 0.005 and 2 μ and an average fiber length between 5 and 1000 μ. 4. The method according to claim 2 or 3, characterized in that a binder is also used for the coating dispersion.